Regarding a conventional rotating electric machine comprised of a rotor and a stator, the stator is made up of a stator core having a plurality of slots formed therein and a coil whose wire is wound around teeth provided between the slots. The rotor is made up of a rotor core having a plurality of electromagnetic steel plates stacked on each other, a permanent magnet generating a magnetic force, and a shaft serving as a rotation shaft. Electric power is supplied to the coil to cause magnetic fields to be generated. According to the generated magnetic fields, a flow of magnetic flux is generated between the rotor and the stator, thereby providing a rotational force to the rotor. In the rotor, the permanent magnet is inserted into an opening provided in the rotor core. End plates are provided to sandwich the rotor core in the direction of the rotation shaft of the rotor.
As a rotating electric machine structured in the above-described manner, Japanese Patent Laying-Open No. 2003-134705, for example, discloses a rotor structure of an electric motor having end plates made of a magnetic material and preventing short-circuit of magnetic flux generated from terminals of a permanent magnet. This electric motor has its rotor structure including, around its rotation shaft, a rotor iron core structured by stacking a plurality of magnetic elements in the axial direction of the rotation shaft and rotating together with the rotation shaft, and including therearound, end plates provided on both sides with respect to the axial direction of the rotation shaft of the rotor iron core for holding the rotor iron core. In the rotor iron core and end plates, a through hole into which the permanent magnet is inserted is provided in the axial direction of the rotation shaft. The permanent magnet has its end faces in the axial direction of the rotation shaft that are substantially coplanar with respective outer faces of the end plates in the same axial direction.
Regarding the rotor structure of the electric motor disclosed in the aforementioned publication, the end faces of the permanent magnet in the axial direction of the rotation shaft are substantially coplanar with respective outer faces of the end plates in the same axial direction. Therefore, even when the end plates are made of a magnetic material, the magnetic flux generated from the vicinity of the terminals of the permanent magnet is directed through the end plates toward the stator located around the rotor. Thus, short circuit of the magnetic flux can be prevented. While short circuit of the magnetic flux is prevented, the end plates can be made of a magnetic material and accordingly an increase in material cost can be avoided.
Since the rotor is provided opposite to the stator, there arises a problem of a short distance between the end plates provided on respective ends of the rotor in the direction of the rotation shaft and the coil ends of the coil wound around the stator core. As electric power is supplied to the coil while the rotating electric machine is operating, an insufficient distance between the end plates and the coil ends causes arc discharge to be generated, resulting in the possibility of peeling of an insulating coating of the coil due to heat generated by the discharge. In the rotor structure disclosed in the aforementioned publication, the distance between the end plates and the coil ends is not taken into consideration. Therefore, such a problem as described above still could arise.
Further, for the purpose of keeping an appropriate distance between the end plates and the coil ends, the end plates may be made thinner or the outer diameter of the end plates may be reduced. However, if the end plates are made thinner, the strength of the whole end plates deteriorates to weaken the force of holding the rotor core. Further, if the outer diameter of the end plates is decreased, the force exerted by the end plates on the rotor core is not uniform. In particular, when the rotor core is made up of a plurality of electromagnetic steel plates, the electromagnetic steel plates could deform.